Re: [lustre-discuss] Issues regarding corss-version mounting of MDT

Sat, 07 Feb 2026 20:31:32 -0800 

Andreas, thanks for your reply.

The MDTs were originally created using Lustre 2.15.4. In my case, I 
accidentally mounted one of the MDTs with Lustre 2.16.1. The system has two 
MDTs in total: one remained untouched by 2.16.1, while the other was mounted 
once with 2.16.1.

After that, I switched back to Lustre 2.15.4 and mounted both MDTs. At that 
point, some files and directories appeared as “????”. It seemed that some kind 
of inconsistency between the states of the two MDTs caused the issue.

Later, I mounted the second MDT (the one that had not been touched before) with 
2.16.1 as well, and then switched back to 2.15.4 to mount both MDTs. After 
this, the problem was resolved.

I’m curious about what kinds of inconsistencies between the MDTs might have led 
to this behavior.

Thanks in advance for your insights.


Cheers，
Huijun




         Original
         
       
From: Andreas Dilger <[email protected]&gt;
Date: Feb 7, 2026 08:10
To: Huijun Wu <[email protected]&gt;
Cc: lustre-discuss <
&gt;
Subject: Re: [lustre-discuss] Issues regarding corss-version mounting of MDT



       
On&nbsp;Feb&nbsp;3,&nbsp;2026,&nbsp;at&nbsp;06:01,&nbsp;Huijun&nbsp;Wu&nbsp;<[email protected]&gt;&nbsp;wrote:
&gt;&nbsp;I&nbsp;recently&nbsp;encountered&nbsp;an&nbsp;issue&nbsp;related&nbsp;to&nbsp;cross-version&nbsp;mounting&nbsp;of&nbsp;an&nbsp;MDT.
&gt;&nbsp;After&nbsp;an&nbsp;MDS&nbsp;crash,&nbsp;I&nbsp;rebooted&nbsp;the&nbsp;MDS&nbsp;and&nbsp;accidentally&nbsp;mounted&nbsp;an&nbsp;MDT&nbsp;that&nbsp;was&nbsp;originally&nbsp;created&nbsp;and&nbsp;used&nbsp;with&nbsp;Lustre&nbsp;2.15.4&nbsp;using&nbsp;Lustre&nbsp;2.16.1.&nbsp;After&nbsp;this,&nbsp;I&nbsp;noticed&nbsp;that&nbsp;many&nbsp;files&nbsp;and&nbsp;directories&nbsp;were&nbsp;shown&nbsp;as&nbsp;“????”&nbsp;on&nbsp;the&nbsp;client&nbsp;side.
&gt;&nbsp;I&nbsp;then&nbsp;ran&nbsp;lfsck&nbsp;on&nbsp;this&nbsp;MDT,&nbsp;and&nbsp;found&nbsp;that&nbsp;some&nbsp;directories&nbsp;that&nbsp;originally&nbsp;belonged&nbsp;to&nbsp;this&nbsp;MDT&nbsp;disappeared&nbsp;entirely.
&gt;&nbsp;Any&nbsp;recommendations&nbsp;on&nbsp;how&nbsp;to&nbsp;analyze,&nbsp;recover,&nbsp;or&nbsp;mitigate&nbsp;this&nbsp;issue?

There&nbsp;definitely&nbsp;shouldn't&nbsp;be&nbsp;any&nbsp;issues&nbsp;upgrading&nbsp;from&nbsp;a&nbsp;2.15&nbsp;MDT&nbsp;to&nbsp;a&nbsp;2.16
MDT,&nbsp;and&nbsp;this&nbsp;is&nbsp;tested&nbsp;regularly&nbsp;during&nbsp;normal&nbsp;Lustre&nbsp;development.

Did&nbsp;you&nbsp;have&nbsp;any&nbsp;unusual&nbsp;features&nbsp;enabled&nbsp;in&nbsp;Lustre&nbsp;or&nbsp;ldiskfs?&nbsp;&nbsp;Was&nbsp;the
filesystem&nbsp;originally&nbsp;formatted&nbsp;with&nbsp;2.15,&nbsp;or&nbsp;was&nbsp;it&nbsp;formatted&nbsp;with&nbsp;an
older&nbsp;version&nbsp;and&nbsp;upgraded&nbsp;already?&nbsp;&nbsp;Were&nbsp;there&nbsp;error&nbsp;messages&nbsp;on&nbsp;the&nbsp;MDS
or&nbsp;client&nbsp;console&nbsp;when&nbsp;accessing&nbsp;the&nbsp;problematic&nbsp;files?

Cheers,&nbsp;Andreas
---
Andreas&nbsp;Dilger
Principal&nbsp;Lustre&nbsp;Architect
[email protected]
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